1. Field of the Invention
The invention relates to a method of manufacturing passive integrated optical devices form polymeric materials for optical fiber networks employing glass fibers or polymer fibers as transmission media, and further relates to devices and molded pieces manufactured according to the method. A "molded piece" as used herein will be understood to mean a plastic article manufactured from a polymeric material by means of a casting or molding operation. The functional device for optical fiber network (FONs) is comprised of such a molded piece along with optical fiber pigtails which are to be coupled, and, possibly, a cover plate.
The aim of the invention is to provide more economical means of manufacturing such devices without detrimentally affecting the usable characteristics of the device.
FONs are becoming continually more important in communications engineering. For communications in the long-distance range and medium-distance range, the transmission medium principally used is single mode fibers comprised of quartz. In the short-distance range and in sensor networks, multimode fibers comprised of quartz or polymeric material are principally used.
FONs are comprised of optical fibers, active components (senders and receivers), controllable components (e.g. switches and modulators), and passive components (e.g. branches, couplers, interferometer structures, wavelength multiplexers, and wavelength demultiplexers). The manufacture of these components has heretofore been costly.
2. Description of the Related Art
It is known to manufacture passive components comprising miniaturized components from geometrical optics, such as lenses, prisms, and mirrors (Lutzke, D., 1986, "Lichtwelienleitertechnik", pub. Pflaum-Verlag, Munich). This miniaturization is subject to limits, in practice.
In Eur. Pat. Appl. 0,366,110, the manufacture of couplers comprised of glass optical fibers is described. The protective sheathing is removed from the optical fibers and the fibers are positioned in proximity and may be twisted together. Under tension they are fused together at a certain temperature. With the use of suitable fibers, multimode or single mode fiber couplers can be manufactured. For a 1.times.N coupler with N&gt;2, a plurality of 1.times.2 couplers are connected in a sequence. This consumes excessive space, and is costly.
Eur. Pat. Appl. 0,315,874 discloses optical couplers for polymer optical fibers wherein 2-1000 polymer optical fibers are oriented in the same direction and bundled together. The fibers may be twisted together over a certain longitudinal distance. A piece of heat-shrinkable plastic tube is pushed over the node. After the heat-shrinkable tube is heated, the fibers are in a state of being tightly bundled together or fused together. The node can be stretched.
In Eur. Pat. Appl. 0,290,329, the manufacture of integrated optical single mode waveguide structures is described. The principle of wave guiding on the substrate by means of a strip waveguide, and the lithographic manufacturing process, allow integration and simultaneous manufacture of diverse optical functions on a substrate. Coupling of optical fibers with integrated optical waveguides manufactured by the described method is costly in terms of resources and finances.
In Eur. Pat. Appl. 0,451,549, optical couplers comprised of polymers, for multimode polymer FONS, are described which couplers are manufactured by injection molding. The coupler element is solid and of a single unit construction, and may be coated with a polymer having a lower index of refraction than the coupler. In the manufacturing method a polymer melt is injected into an injection mold which is comprised of two or more mold elements. After the melt solidifies, the finished coupler element comprised of the junction region with the pigtails of the optical fibers is removed from the mold. According to another method, channels are formed in the surface of a plastic plate, by injection molding, and the optical fibers are inserted in said channels. The void space between the fiber pigtails is filled with castable resin. The injection mold is fabricated by machining or spark erosion, followed by polishing. The channels for the optical fibers have a square or round cross section, and a diameter or side length of 0.1-3 mm.
Eur. Pat. Appl. 0,324,492 discloses a coupler for optical fibers which coupler is comprised of a stepped base plate which bears, on two sides, a number of "trenches" for introducing the ends of the waveguiding means. In the middle part of the plate the coupling structures are produced by a photolithographic process which may involve a plurality of stages.
In Eur. Pat. Appl. 0,420,173 a method of manufacturing finned waveguide structures from polymeric materials is described wherein a metal mold is filled with a liquid material which is cured by the action of energetic radiation. The time consumed in this method is typically greater than with, e.g., injection molding methods.
The known methods are characterized by a relatively costly technology wherein the waveguide structures and the alignment structures for the optical fibers are produced in or on the substrate. Some of the known methods allow only manufacture in the form of a single unit structure, or require special machinery. Some of the couplers have relatively high transmission losses and/or are not mechanically robust. For coupling of optical fibers to an integrated optical switching circuit, heretofore no satisfactorily economical and time-stable solution has been discovered. Previously it was difficult to produce the required vertical and horizontal cavity structures in precise positions for alignment with the relatively small waveguide structures. Only components for multimode polymeric FONs could be successfully produced with the use of economical mold processes, under known technology. Heretofore there was no known suitable transition means between a fiber alignment structure and a waveguide structure for multimode glass optical fibers or single mode glass optical fibers, for adjusting for the differing diameters of fiber cores and cladding.